Clutches engage and disengage two moving parts relative to one another. In vehicles, clutches are used to change gears to control the amount of power that is transferred from the vehicle's engine to the transmission to make the vehicle move. In particular, a pressure plate removably engages a drive member attached to a clutch flywheel connected to the engine crankshaft. Disengagement of the clutch by depressing the clutch pedal releases the pressure plate from contact with the drive member to allow the gears to be changed in the vehicle.
Over time, components of clutches wear down from constant engagement and disengagement during use. In order to allow the clutch to effectively work, the components of the clutch need to be adjusted to ensure that the pressure plate remains in frictional contact relative to the flywheel when the clutch is not engaged.
Heretofore, it has been known to use manual and self-adjusting clutches to accommodate for the wear in the driven member to increase the life and effectiveness of the clutch. A self-adjusting clutch is intended to make the internal adjustment automatically as the components wear and thus reduce the maintenance, and thus downtime and related expenses, for the vehicle.
One form of a self-adjusting clutch comprises a pair of opposing cam rings having a plurality of corresponding ramps with serrations thereon, wherein the ramps of the cam rings and their serrations engage each other when the clutch is engaged to lock the internal components of the clutch in place relative to one another. After a period of use, wear on the friction surface of the driven member causes the distance between the pressure plate and driven member to increase. The additional distance causes one of the cam rings to rotate relative to the other cam ring when the clutch is not engaged to compensate for wear on the friction surface of the driven member of the clutch. Examples of self-adjusting clutches includes those disclosed in U.S. Pat. No. 5,566,804, the entirety of which is hereby incorporated by reference.
While such self-adjusting clutches work, problems have arisen during their use and operation in the field. In particular, it has been known for the cam rings to jump when there is a sudden impact to a vehicle (e.g., when a truck hits a loading dock when backing up), thereby causing an overadjustment of the cam rings due to the increased distance caused by the impact. The overadjustment shortens the life of the clutch and diminishes its value.